The present invention relates generally to vehicle steering and suspension systems and, in particular, to strut-type vehicle steering and suspension systems.
Many automotive vehicles today employ a type of front suspension commonly known as a McPherson strut suspension. This type of suspension includes a strut assembly, with an upper strut mount affixed to a vehicle frame or body and a lower end affixed to a steering knuckle. The lower end of the steering knuckle also attaches, via a ball joint, to a lower control arm, which is hinged to the vehicle frame or body. While this conventional suspension works well for many vehicle applications, it creates a spindle length—the distance from the wheel center plane to steer axis along the wheel rotation axis—that is larger than desirable. The steer axis is located away from the wheel center plane due to the fact that, with this suspension, it is defined by the ball joint and upper strut mount location. This large spindle axis undesirably increases steering system loads when tractive forces (front wheel drive), road profile impact forces, or rotating assembly imbalance forces are applied. This undesirable increase in steering system loads is particularly noticeable on front wheel drive vehicles with high-powered engines. On these types of vehicles, traction steer concerns may become apparent during combined acceleration and turn events.
While a different type of suspension may be provided for such high-powered vehicles, this may require substantial changes to the vehicle's frame or body to accommodate this different suspension. The cost to make these changes on an existing vehicle may be prohibitive, leaving one only the choice of the conventional suspension. Consequently, it is desirable to improve the suspension and steering performance on vehicles where the frame or body has already been designed specifically for a McPherson strut suspension without having to substantially modify the frame or body of that vehicle, and while remaining generally within the packaging space of the conventional McPherson strut suspension.
Some have attempted to provide a different suspension that may be employed with a vehicle that has been designed generally for a strut suspension while also shortening the spindle length. Generally, these attempts are directed to creating a different steering axis than is defined by a conventional McPherson strut-type suspension. While the steering axis may change, these designs have had undesirable drawbacks. For some, the design of the modified steering and suspension system is much more complicated, costly and/or much heavier than is desirable. For others, the design may have less than desirable durability characteristics, or be more limited in the types and amount of adjustments that can be made to tune the suspension to its most desirable performance characteristics.
It is desirable, therefore, to provide a steering and suspension system that can be employed with a vehicle frame or body designed for a McPherson strut suspension, yet has a shorter spindle length to provide improved performance, while also minimizing other drawbacks, such as being cost effective and providing good durability over the life of the vehicle.